1. Field of the Invention
The present invention relates to a process for manipulating any polyhydroxy compound bearing two or more primary and secondary hydroxyl groups to expose only the primary hydroxyl groups, while blocking all interfering secondary hydroxyl groups as their methyl or other alkyl ethers. More particularly, the present invention relates to the synthesis of 2,3,3',4,4'-penta-O-methylsucrose by using the aforedescribed method.
2. Description of the Prior Art
In the past, many attempts have been made to employ carbohydrates for the development of well-characterized novel polymers of some practical significance. The use of sugars and their derivatives in the production of polymers is of growing interest since polymers containing mono- or disaccharides in their main chain or as grafted pendant groups or chains display useful and unique properties such as hydrophilicity, chirality, biological activity, biodegradability, and the like. Furthermore, most sugars are available at economical prices and are industrially produced in large quantities by cultivation in plants and microorganisms, followed by chemical isolation or by degradation of plant waste material followed by isolation. For instance, sucrose is produced on a scale that is larger than any other pure organic chemical, world-wide.
The major problem associated with the use of carbohydrates for developing polymers is the similar reactivity of the primary and secondary hydroxyl groups on the carbohydrate moiety. Hence, when carbohydrates are polymerized non-enzymatically with other monomers, the resulting polymer products are often a mixture of linear, cross-linked and branched chain products. This is due to the reaction of both the primary and secondary hydroxyl groups in the carbohydrate moiety with electrophilic groups in the other monomer.
Many attempts have been made in the past towards polymerizing carbohydrates such as those attempts described by N. Ogata et al in J. Polym. Sci., Polym. Chem. Ed., Vol. 19, p. 2609 (1981) and Vol. 22, p. 739 (1984); and S. K. Dirlikov, "Monomers and Polymers Based on Mono and Disaccharides", Pacific Polymer Preprints, First Pacific Conference, Dec. 12-15, 1989, Volume 1, pp. 113-114.
Although Dirlikov, supra, claims that high molecular weight polymers have been made, no proof has been shown that these polymers are strictly linear and do not contain additional cross-linked or branched chain polymers and that only the primary hydroxyl groups react thereby forming a strictly linear polymer.
Sucrose used as a starting carbohydrate for the production of carbohydrate polymers would be ideal since it is produced in vast quantities and is low in price. To synthesize intermediate sucrose derivatives for further use in the production of novel polymers using sucrose as a starting compound is difficult due to the reactivity of the primary hydroxyl groups at carbons 6, 1' and 6' and the remaining five secondary hydroxyl groups.
One such sucrose intermediate is 2,3,3',4,4'-penta-O-methylsucrose having the structure: ##STR1##
The compound of structure (I) is useful as an intermediate in the synthesis of other sucrose derivatives that can be used to synthesize various polymers. This compound has been ambiguously reported by McKeown et al in the Canadian Journal of Chemistry, Vol. 35 (1957), p. 992, and subsequently prepared in moderate yields by O'Donnell and Richards as described in the Australian Journal of Chemistry, Vol. 25 (1972), pp. 407-412.
However, heretofore, 2,3,3',4,4'-penta-0-methylsucrose has been synthesized by O'Donnell and Richards through several intermediate compounds such as 1',6,6'-tri-O-tritylsucrose, 1',6,6'-tri-O-trityl-2,3,3',4,4'-penta-O-acetylsucrose, and 1',6,6'-tri-O-trityl-2,3,3',4,4'-penta-O-methylsucrose. The final product of 2,3,3',4,4'-penta-0methylsucrose was isolated in the final step by chromatography through amberlite resins, which tend to epimerize the C-1 of the glucopyranoside due to the acidity of these resins. Moreover, the total yield for the synthesis of 2,3,3',4,4'-penta-0-methylsucrose is about 26%, while the yield in the final step is about 79% by using the method described by O'Donnell and Richards.
It has now surprisingly been discovered that 2,3,3',4,4'-penta-O-methylsucrose can be synthesized by eliminating the intermediate compound of 1',6,6'-tri-O-trityl-2,3,4',4,4'-penta-O-acetylsucrose. Moreover, by replacing the amberlite resins with silica gel, the synthesized product does not epimerize at the C-1 position. A marked increase in yield of penta-0-methylsucrose (e.g., yields of up to 97%) is also produced by the present process, thus leading to an intermediate that can be readily produced for use in polymer synthesis.